The present invention relates generally to an electronic typewriter having calculating and displaying capabilities, and more particularly to an electronic typewriter which is capable of: displaying and editing a succession of characters which are entered through a keyboard and which include numerals and one or more arithmetic operator symbols designating an arithmetic operation; capable of performing the designated arithmetic operation; and further capable of printing a result of the arithmetic operation as well as the entered statement.
In a known electronic typewriter, it is possible to print desired characters such as alphabetic letters and numerals which are entered through a keyboard. Such printing may be effected on a desired kind of paper, for example, on a form with spaces left for the insertion of information, by way of moving a carriage along a line of printing to fill the spaces with desired information. The information to be inserted may often contain an arithmetic statement including numerical values, and an arithmetic symbol to designate a kind of mathematical operation. In such instance, it is required to solve a mathematical problem which is defined by such arithmetic statement, and to print a result of the arithmetic operation together with the entered arithmetic statement. Thus, the operator of the typewriter has to use a desktop or portable electronic calculator for obtaining the arithmetic result and then enter the obtained result so that the result is printed following the arithmetic statement. Those steps of calculation and additional data entry will require extra time and consequently reduce printing efficiency.
On the other hand, commonly used desktop calculators are capable of calculating according to entries of numerical data and an arithmetic symbol, and displaying the arithmetic expression including the result of the calculation. However, those calculators suffer low printing capability and recordability in terms of usable characters and print paper, as well known in the art.
To meet the above stated requirement and overcome the drawbacks recognized in the art of calculating, displaying and printing an arithmetic expression, the present applicant developed an electronic typewriter having calculating capability, which is the subject matter of a copending U.S. application Ser. No. 426,136 filed Sept. 28, 1982, the disclosure of which is hereby incorporated by reference.
The typewriter disclosed in the above identified application is capable of performing an arithmetic operation which is defined by an arithmetic symbol or symbols and numerical values entered in the form of combined numerals and letters, and which is further capable of displaying and printing a result of the arithmetic operation following the entered arithmetic statement. This typewriter is constructed to comprise: a keyboard; arithmetic means for performing an arithmetic operation designated by at least one of the arithmetic operator keys, based on plural sets of numerical data each representing a numerical value and entered through numeral keys; main control means for selecting the numerical data as operands from among successive sets of data entered through the letter, numeral and arithmetic symbol keys including an equality key as well as the arithmetic operator keys, such that only the set of numerical data which is entered last prior to each operation of any one of the arithmetic symbol keys is regarded as one of the operands, the main control means directing the arithmetic means to perform the arithmetic operation based on the selected sets of numerical data, and reading out a result of the arithmetic operation from the arithmetic means; and a printing device printing a succession of characters entered by the letter, numeral and arithmetic symbol keys, and the result of arithmetic operation read out by the main control means, the result being printed following the entered succession of letters. The above typewriter may further include a display unit which indicates the entered characters.
In the typewriter having the above arrangement, the entered characters are printed as they are shifted out of the display unit after the display unit has overflowed with the entered characters, and the displayed characters are all printed when a carriage return key is depressed. More specifically, leading characters on the display unit are automatically printed one after another when subsequent entries of characters have overflowed the display unit. This means that the entered data may not be corrected or edited after the digit capacity of the display unit has been reached, because the previously entered characters have been already printed. Further, the automatic printing of the above arrangement will prevent the typewriter from being used simply as an ordinary electronic calculator when it is desired to merely obtain a result of a mathematical statement or expression without having to print out the result of calculation as well as the entered statement. Another inconvenience experienced on the same typewriter lies in that the entered characters may not be printed as soon as they have been entered as in an ordinary typewriter.